Molybdenum silicide (MoSi2) based materials are well known for high temperature furnaces applications. Heating elements made of these materials show good performance at high temperatures, such as above 1800° C., in air because of the formation of a protective silicon dioxide (silica) layer.
When heating molybdenum silicide based materials in air, both the molybdenum and the silicon will be oxidized. The molybdenum oxide will become volatile and evaporate and the silicon will form an oxide layer on the material, which will prevent the material from corrosion and other wear degradations. However, at low temperatures, the molybdenum oxide will remain in the surface layer and will therefore disturb the formation of a continuous silicon dioxide layer. This may lead to a continuous consumption of the material (MoSi2) of the heating element. This phenomenon is called “pesting” or “pest”.
It has been shown that chromium-additions to heating elements comprising MoSi2 will reduce the degradation of the heating material at 450° C. It has also been indicated that formation of chromium molybdate will slow down the material consumption in heating elements comprising chromium alloyed MoSi2.
Even though all this progress made for heating elements based on MoSi2, there exists still a problem, especially in industrial furnaces, with the degradation of MoSi2 based heating element. In industrial furnaces, there will be different temperature zones, in general zones having high temperatures and zones having low temperature. Thus, the MoSi2 based heating elements contained therein will also have different temperature zones. In the high temperature zones, there will be no problem with pesting as the silica is formed immediately. However, in the low temperature zones, there will be problems with pesting, which means that these parts of the MoSi2 based heating element will be exposed to corrosion etc., which eventually will lead to heating element failure. Another problem associated with pesting is that when the heating element fails, parts of the surface oxide may fall into the furnace and contaminate the material being heated.
The aim of the present disclosure is to eliminate or at least reduce the above-mentioned problems.